This invention relates to a multi-spindle fastening apparatus having a multi-spindle fastening head for effecting simultaneous fastening operations on a workpiece having plural portions to be fastened, and is more particularly directed such a replaceable head apparatus wherein the plural fastening head thereof may be replaced one with another in compliance with changes in the kinds of workpieces.
A known apparatus of this kind is disclosed in Japanese Patent Application Sho No. 57-85029 comprising a supporting column provided on the circumference thereof with an annular rail means, and a plurality of multi-spindle fastening heads supported on the annular rail means. A portion of annular rail means is formed into a movable rail means supported on an elevating frame. An index means is provided on the supporting column so that any desired one of those plural multi-spindle fastening heads may be selected to be positioned on the movable rail means by the index means. The selected fastening head on the movable rail means may be lowered by lowering the elevating frame, to a working station provided on one side of a lower portion of the supporting column for effecting a fastening operation of a workpiece.
It has been usual with this kind of apparatus that plural nut runners are mounted on each of the multi-spindle fastening heads, and that the elevating frame is provided thereon with a connecting head which is connectible to and disconnectible from the fastening head selected on the movable rail means so that the selected fastening head may be connected through the connecting head to a power source such as a nut runner driving air source or the like. This arrangement, however, has various disadvantages described below.
(i) Because of the fact that plural nut runners are mounted on each of the fastening heads, each head is increased in cost as well as in weight. As a result of this increase in weight, the index means is required to be a high output large-sized one which results in an increase in installation cost.
(ii) From a viewpoint of restriction as to space and weight, each nut runner and each fastening member such as a socket or the like on each fastening head must be disposed to be in alignment one with another, and in direct coupling relationship. Accordingly, if an interval between portions to be fastened is smaller than an interval necessary for avoiding mutual interferences of adjacent nut runners, it becomes impossible to effect a fastening operation.
(iii) In a case where a highly accurate fastening torque control is needed, nut runners having a torque transducer operable by a weak electrical current are mounted on the fastening head. In such a case, an electric connector for an external electric power source is required to be provided between the fastening head and the connecting head. However, it often happens that difficulties with such a connector resulting from bad electric contact due to dust, abrasion or the like occur. Accordingly, unreliable torque control results.